There are various kinds of existing toy cars, and most of them are conventional toy cars running on a single side, i.e. wheels are disposed at the bottom of a car body to make a toy car run. The toy cars have simple designs of transmission structures and single functions, and lack of interestingness. Currently, there is a kind of toy car that is a double-sided toy car, this kind of toy car is provided with wheels both at the top and bottom of its car body, so that the double-sided toy car can run on an obverse side and a reverse side, thus a sealed track for running the double-sided toy car is designed, which is a track body including an upper track for upper wheels of the double-sided car to touch and a lower track for lower wheels of the double-sided car to touch, the double-sided car can run within the sealed track freely. However since a transmission structure of the existing double-sided toy car is cumbersome and both the upper and lower wheels of the double-sided toy car are keeping in touch with the upper and lower tracks of the sealed track, when the double-sided is turning vertically, front wheels enter a vertical turning segment firstly so that an entire forepart of the car body is raised, at the time a relative displacement between the upper and lower wheels of rear wheels will appear, however since that a height of the track is constant, the double-sided toy car is stuck and unable to move frequently. There are three existing methods for handling this. The first one is to omit the design of the vertical turning segment of the sealed track, which means that the distinct performance of the double-sided car running within the sealed track cannot be shown. The second one is to reduce the height of the double-sided car or increase the up-down height of the sealed track, that is, the upper wheels of the double-sided car cannot touch the upper track, thus leaving an enough turning space for the double-sided car at the vertical turning segment so as to achieve the vertical turning, however since there is a gap between the double-sided car and the track, and the double-sided car cannot run on the vertical track and cannot run smoothly within the track because of the gap. The third one is to make the upper and lower wheels of the double-sided car be capable of retracting relative to each other, which can be achieved by hanging a spring on an axle and a car body, thus ensuring that the upper and lower wheels can be retracted when being squeezed at the vertical turning segment, so that the double-sided car cannot to be stuck. However such designs further increase the weight of the double-sided car and the production cost, and the transmission structure is more complicated, a driving force of the double-sided car during the retracting process can be influenced, moreover the spring may be unable to be retracted during use, which means that the double-sided car is stuck at the vertical turning segment as well.